If you have been given the option to carry 15 failed non-core credits (referred to as condonement in the Rules of Assessment) and to trail 15 failed credits, this means you can progress to your next year of studies and simultaneously undertake reassessment in 15 failed non-core credits, known as trailing reassessment. You will have no further reassessment in the 15 failed credits that your carry.
For further information on carrying and trailing credits and their impact on your further studies, please see the relevant outcome pages linked below: